The present invention is specifically concerned with bioimplants for mammals. More broadly the invention has application to any situation when a material is needed for contact with living mammalian tissue wherein a substantially non-irritating or minimal biological response is needed.
In general every foreign material placed in the body causes at least some slight degree of response which may be thought of largely as the body's defense against invasion by foreign substances.
Polyurethane surgical dressings have been proposed in the past as represented by U.S. Pat. Nos. 3,978,266 and 3,978,855. Patent 3,978,855 mentions at the top of Col. 2 that polyurethane foam cell structures cause inflammatory cells to be attracted when impressed into the dermis or when the polyurethane material breaks away and comes to lie in the developing connective tissue under the epidermis.